DESCRIPTION

crypto is a framework for drivers of cryptographic hardware to register
with the kernel so “consumers” (other kernel subsystems, and users
through the /dev/crypto device) are able to make use of it. Drivers
register with the framework the algorithms they support, and provide
entry points (functions) the framework may call to establish, use, and
tear down sessions. Sessions are used to cache cryptographic information
in a particular driver (or associated hardware), so initialization is not
needed with every request. Consumers of cryptographic services pass a
set of descriptors that instruct the framework (and the drivers
registered with it) of the operations that should be applied on the data
(more than one cryptographic operation can be requested).
Keying operations are supported as well. Unlike the symmetric operators
described above, these sessionless commands perform mathematical
operations using input and output parameters.
Since the consumers may not be associated with a process, drivers may not
sleep(9). The same holds for the framework. Thus, a callback mechanism
is used to notify a consumer that a request has been completed (the
callback is specified by the consumer on an per-request basis). The
callback is invoked by the framework whether the request was successfully
completed or not. An error indication is provided in the latter case. A
specific error code, EAGAIN, is used to indicate that a session number
has changed and that the request may be re-submitted immediately with the
new session number. Errors are only returned to the invoking function if
not enough information to call the callback is available (meaning, there
was a fatal error in verifying the arguments). For session
initialization and teardown there is no callback mechanism used.
The crypto_newsession() routine is called by consumers of cryptographic
services (such as the ipsec(4) stack) that wish to establish a new
session with the framework. On success, the first argument will contain
the Session Identifier (SID). The second argument contains all the
necessary information for the driver to establish the session. The third
argument indicates whether a hardware driver (1) should be used or not
(0). The various fields in the cryptoini structure are:
cri_alg Contains an algorithm identifier. Currently supported
algorithms are:
CRYPTO_AES_CBC
CRYPTO_ARC4
CRYPTO_BLF_CBC
CRYPTO_CAMELLIA_CBC
CRYPTO_CAST_CBC
CRYPTO_DES_CBC
CRYPTO_3DES_CBC
CRYPTO_SKIPJACK_CBC
CRYPTO_MD5
CRYPTO_MD5_HMAC
CRYPTO_MD5_KPDK
CRYPTO_RIPEMD160_HMAC
CRYPTO_SHA1
CRYPTO_SHA1_HMAC
CRYPTO_SHA1_KPDK
CRYPTO_SHA2_256_HMAC
CRYPTO_SHA2_384_HMAC
CRYPTO_SHA2_512_HMAC
CRYPTO_NULL_HMAC
CRYPTO_NULL_CBC
cri_klen Specifies the length of the key in bits, for variable-size key
algorithms.
cri_mlen Specifies how many bytes from the calculated hash should be
copied back. 0 means entire hash.
cri_key Contains the key to be used with the algorithm.
cri_iv Contains an explicit initialization vector (IV), if it does not
prefix the data. This field is ignored during initialization.
If no IV is explicitly passed (see below on details), a random
IV is used by the device driver processing the request.
cri_next Contains a pointer to another cryptoini structure. Multiple
such structures may be linked to establish multi-algorithm
sessions (ipsec(4) is an example consumer of such a feature).
The cryptoini structure and its contents will not be modified by the
framework (or the drivers used). Subsequent requests for processing that
use the SID returned will avoid the cost of re-initializing the hardware
(in essence, SID acts as an index in the session cache of the driver).
crypto_freesession() is called with the SID returned by
crypto_newsession() to disestablish the session.
crypto_dispatch() is called to process a request. The various fields in
the cryptop structure are:
crp_sid Contains the SID.
crp_ilen Indicates the total length in bytes of the buffer to be
processed.
crp_olen On return, contains the total length of the result. For
symmetric crypto operations, this will be the same as the
input length. This will be used if the framework needs to
allocate a new buffer for the result (or for re-formatting
the input).
crp_callback This routine is invoked upon completion of the request,
whether successful or not. It is invoked through the
crypto_done() routine. If the request was not successful,
an error code is set in the crp_etype field. It is the
responsibility of the callback routine to set the
appropriate spl(9) level.
crp_etype Contains the error type, if any errors were encountered, or
zero if the request was successfully processed. If the
EAGAIN error code is returned, the SID has changed (and has
been recorded in the crp_sid field). The consumer should
record the new SID and use it in all subsequent requests.
In this case, the request may be re-submitted immediately.
This mechanism is used by the framework to perform session
migration (move a session from one driver to another,
because of availability, performance, or other
considerations).
Note that this field only makes sense when examined by the
callback routine specified in crp_callback. Errors are
returned to the invoker of crypto_process() only when
enough information is not present to call the callback
routine (i.e., if the pointer passed is NULL or if no
callback routine was specified).
crp_flags Is a bitmask of flags associated with this request.
Currently defined flags are:
CRYPTO_F_IMBUF The buffer pointed to by crp_buf is an
mbuf chain.
CRYPTO_F_IOV The buffer pointed to by crp_buf is an
uio structure.
CRYPTO_F_REL Must return data in the same place.
CRYPTO_F_BATCH Batch operation if possible.
CRYPTO_F_CBIMM Do callback immediately instead of doing
it from a dedicated kernel thread.
CRYPTO_F_DONE Operation completed.
CRYPTO_F_CBIFSYNC Do callback immediately if operation is
synchronous.
crp_buf Points to the input buffer. On return (when the callback
is invoked), it contains the result of the request. The
input buffer may be an mbuf chain or a contiguous buffer,
depending on crp_flags.
crp_opaque This is passed through the crypto framework untouched and
is intended for the invoking application’s use.
crp_desc This is a linked list of descriptors. Each descriptor
provides information about what type of cryptographic
operation should be done on the input buffer. The various
fields are:
crd_iv The field where IV should be provided when the
CRD_F_IV_EXPLICIT flag is given.
crd_key When the CRD_F_KEY_EXPLICIT flag is given, the
crd_key points to a buffer with encryption or
authentication key.
crd_alg An algorithm to use. Must be the same as the
one given at newsession time.
crd_klen The crd_key key length.
crd_skip The offset in the input buffer where processing
should start.
crd_len How many bytes, after crd_skip, should be
processed.
crd_inject Offset from the beginning of the buffer to
insert any results. For encryption algorithms,
this is where the initialization vector (IV)
will be inserted when encrypting or where it
can be found when decrypting (subject to
crd_flags). For MAC algorithms, this is where
the result of the keyed hash will be inserted.
crd_flags The following flags are defined:
CRD_F_ENCRYPT
For encryption algorithms, this bit is set
when encryption is required (when not set,
decryption is performed).
CRD_F_IV_PRESENT
For encryption algorithms, this bit is set
when the IV already precedes the data, so
the crd_inject value will be ignored and
no IV will be written in the buffer.
Otherwise, the IV used to encrypt the
packet will be written at the location
pointed to by crd_inject. The IV length
is assumed to be equal to the blocksize of
the encryption algorithm. Some
applications that do special “IV cooking”,
such as the half-IV mode in ipsec(4), can
use this flag to indicate that the IV
should not be written on the packet. This
flag is typically used in conjunction with
the CRD_F_IV_EXPLICIT flag.
CRD_F_IV_EXPLICIT
For encryption algorithms, this bit is set
when the IV is explicitly provided by the
consumer in the crd_iv field. Otherwise,
for encryption operations the IV is
provided for by the driver used to perform
the operation, whereas for decryption
operations it is pointed to by the
crd_inject field. This flag is typically
used when the IV is calculated “on the
fly” by the consumer, and does not precede
the data (some ipsec(4) configurations,
and the encrypted swap are two such
examples).
CRD_F_KEY_EXPLICIT
For encryption and authentication (MAC)
algorithms, this bit is set when the key
is explicitly provided by the consumer in
the crd_key field for the given operation.
Otherwise, the key is taken at newsession
time from the cri_key field.
CRD_F_COMP
For compression algorithms, this bit is
set when compression is required (when not
set, decompression is performed).
CRD_INI This cryptoini structure will not be modified
by the framework or the device drivers. Since
this information accompanies every
cryptographic operation request, drivers may
re-initialize state on-demand (typically an
expensive operation). Furthermore, the
cryptographic framework may re-route requests
as a result of full queues or hardware failure,
as described above.
crd_next Point to the next descriptor. Linked
operations are useful in protocols such as
ipsec(4), where multiple cryptographic
transforms may be applied on the same block of
data.
crypto_getreq() allocates a cryptop structure with a linked list of as
many cryptodesc structures as were specified in the argument passed to
it.
crypto_freereq() deallocates a structure cryptop and any cryptodesc
structures linked to it. Note that it is the responsibility of the
callback routine to do the necessary cleanups associated with the opaque
field in the cryptop structure.
crypto_kdispatch() is called to perform a keying operation. The various
fields in the cryptkop structure are:
krp_op Operation code, such as CRK_MOD_EXP.
krp_status Return code. This errno-style variable indicates whether
lower level reasons for operation failure.
krp_iparams Number if input parameters to the specified operation.
Note that each operation has a (typically hardwired)
number of such parameters.
krp_oparams Number if output parameters from the specified operation.
Note that each operation has a (typically hardwired)
number of such parameters.
krp_kvp An array of kernel memory blocks containing the
parameters.
krp_hid Identifier specifying which low-level driver is being
used.
krp_callback Callback called on completion of a keying operation.

DRIVER-SIDEAPI

The crypto_get_driverid(), crypto_register(), crypto_kregister(),
crypto_unregister(), crypto_unblock(), and crypto_done() routines are
used by drivers that provide support for cryptographic primitives to
register and unregister with the kernel crypto services framework.
Drivers must first use the crypto_get_driverid() function to acquire a
driver identifier, specifying the cc_flags as an argument (normally 0,
but software-only drivers should specify CRYPTOCAP_F_SOFTWARE). For each
algorithm the driver supports, it must then call crypto_register(). The
first two arguments are the driver and algorithm identifiers. The next
two arguments specify the largest possible operator length (in bits,
important for public key operations) and flags for this algorithm. The
last four arguments must be provided in the first call to
crypto_register() and are ignored in all subsequent calls. They are
pointers to three driver-provided functions that the framework may call
to establish new cryptographic context with the driver, free already
established context, and ask for a request to be processed (encrypt,
decrypt, etc.); and an opaque parameter to pass when calling each of
these routines. crypto_unregister() is called by drivers that wish to
withdraw support for an algorithm. The two arguments are the driver and
algorithm identifiers, respectively. Typically, drivers for PCMCIA
crypto cards that are being ejected will invoke this routine for all
algorithms supported by the card. crypto_unregister_all() will
unregister all algorithms registered by a driver and the driver will be
disabled (no new sessions will be allocated on that driver, and any
existing sessions will be migrated to other drivers). The same will be
done if all algorithms associated with a driver are unregistered one by
one.
The calling convention for the three driver-supplied routines is:
int (*newsession)(void*, u_int32_t*, structcryptoini*);
int (*freesession)(void*, u_int64_t);
int (*process)(void*, structcryptop*);
int (*kprocess)(void*, structcryptkop*);
On invocation, the first argument to all routines is an opaque data value
supplied when the algorithm is registered with crypto_register(). The
second argument to newsession() contains the driver identifier obtained
via crypto_get_driverid(). On successful return, it should contain a
driver-specific session identifier. The third argument is identical to
that of crypto_newsession().
The freesession() routine takes as arguments the opaque data value and
the SID (which is the concatenation of the driver identifier and the
driver-specific session identifier). It should clear any context
associated with the session (clear hardware registers, memory, etc.).
The process() routine is invoked with a request to perform crypto
processing. This routine must not block, but should queue the request
and return immediately. Upon processing the request, the callback
routine should be invoked. In case of an unrecoverable error, the error
indication must be placed in the crp_etype field of the cryptop
structure. When the request is completed, or an error is detected, the
process() routine should invoke crypto_done(). Session migration may be
performed, as mentioned previously.
In case of a temporary resource exhaustion, the process() routine may
return ERESTART in which case the crypto services will requeue the
request, mark the driver as “blocked”, and stop submitting requests for
processing. The driver is then responsible for notifying the crypto
services when it is again able to process requests through the
crypto_unblock() routine. This simple flow control mechanism should only
be used for short-lived resource exhaustion as it causes operations to be
queued in the crypto layer. Doing so is preferable to returning an error
in such cases as it can cause network protocols to degrade performance by
treating the failure much like a lost packet.
The kprocess() routine is invoked with a request to perform crypto key
processing. This routine must not block, but should queue the request
and return immediately. Upon processing the request, the callback
routine should be invoked. In case of an unrecoverable error, the error
indication must be placed in the krp_status field of the cryptkop
structure. When the request is completed, or an error is detected, the
kprocess() routine should invoked crypto_kdone().

RETURNVALUES

crypto_register(), crypto_kregister(), crypto_unregister(),
crypto_newsession(), crypto_freesession(), and crypto_unblock() return 0
on success, or an error code on failure. crypto_get_driverid() returns a
non-negative value on error, and -1 on failure. crypto_getreq() returns
a pointer to a cryptop structure and NULL on failure. crypto_dispatch()
returns EINVAL if its argument or the callback function was NULL, and 0
otherwise. The callback is provided with an error code in case of
failure, in the crp_etype field.

FILES

sys/opencrypto/crypto.c most of the framework code

SEEALSO

HISTORY

The cryptographic framework first appeared in OpenBSD 2.7 and was written
by Angelos D. Keromytis 〈angelos@openbsd.org〉.

BUGS

The framework currently assumes that all the algorithms in a
crypto_newsession() operation must be available by the same driver. If
that is not the case, session initialization will fail.
The framework also needs a mechanism for determining which driver is best
for a specific set of algorithms associated with a session. Some type of
benchmarking is in order here.
Multiple instances of the same algorithm in the same session are not
supported. Note that 3DES is considered one algorithm (and not three
instances of DES). Thus, 3DES and DES could be mixed in the same
request.